The think tank calls the proposed pathway to citizenship "amnesty," and argues these costs will begin adding up as 11 million immigrants become eligible for welfare services, Medicare and Obamacare. The report acknowledges that households consisting of immigrants without documentation are already using subsidized public services such as education, transportation and public safety.

The report says the problem is most of the immigrants lack the earning power of higher education and would become a burden on the welfare system.

“What the Amnesty proponents are saying is they can take someone from Mexico or Guatemala with a 10th grade education, plunk them into that system and somehow miraculously that person is going to pay more in taxes than they take out in benefits. That’s not only untrue it just profoundly implausible," said report author Robert Rector.

The study is an update to the 2007 report. Although heavily criticized across the aisle, it was credited with helping derail immigration reform that year. Like 2007, the Heritage Foundation’s updated version has been met with instant criticism.

Before its release, a vocal opponent of the 2007 findings, Libertarian think tank Cato Institute, urged them to avoid “the same serious errors":

Count individuals, not households. Heritage counts household use of government benefits, not individual immigrant use. Many unauthorized immigrants are married to U.S. citizens and have U.S. citizen children who live in the same households. Counting the fiscal costs of those native-born U.S. citizens massively overstates the fiscal costs of immigration.

But here is one of the conclusions from the Heritage Foundation’s 2013 study:

Following amnesty, the fiscal costs of former unlawful immigrant households will be roughly the same as those of lawful immigrant and non-immigrant households with the same level of education. Because U.S. government policy is highly redistributive, those costs are very large. Those who claim that amnesty will not create a large fiscal burden are simply in a state of denial concerning the underlying redistributional nature of government policy in the 21st century.

Sen. Jeff Flake (R-Ariz.), part of the bipartisan group of senators who helped craft the immigration bill, also suggested the study was flawed:

Bean said the 2007 Heritage Foundation immigration report got a lot wrong, including not giving enough credit for the immigrants’ contributions to the economy and doing low skill work that others simply won’t do at any cost.

The Heritage Foundation’s findings come during a time when immigration advocates are hoping to squeeze vital votes in the conservative-controlled House.